Products > Test Equipment
Help me choosing new Oscilloscope
nctnico:
--- Quote from: porter on April 09, 2023, 05:30:29 pm ---Too bad that Keysight and Tektronix oscilloscpes are no longer part of these discussions.
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That is mainly because they don't have many products in the US $1000 price range that aren't cut down too much. Still, in a professional setting I'd buy an A brand oscilloscope (and many other types of complex equipment) any time of the day.
tggzzz:
--- Quote from: Performa01 on April 09, 2023, 05:14:36 pm ---
--- Quote from: tggzzz on April 09, 2023, 01:17:36 pm ---
--- Quote ---The sample rate on the other hand has to be twice the max. input frequency in order to satisfy Nyquist.
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No. Or rather the sample rate has to be at least twice the bandwidth of the signal to satisfy Nyquist[1].
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So you are saying "no", only to use the following sentence to repeat what I said in slightly different words?
Oh – did I forget to say "at least"? In a statement where I wanted to stress the fact that oversampling doesn't provide any additional information?
And what is the difference between "max. input frequency" and "bandwidth of the signal"? There is only a difference if we presume that we're not interested in the entire input signal, but only a part of it [1] – which certainly would not be a standard use case.
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The difference, as I'm sure you are aware, is that the "signal" needs to be carefully defined when considering the Nyquist frequency. See the audio on 10MHz carrier example :)
Beginners often don't understand the difference, and too often experienced people don't either - as we've seen in this thread!
--- Quote ---
--- Quote from: tggzzz on April 09, 2023, 01:17:36 pm ---I have a 1972 portable scope (which can be stored underwater!) which takes one sample every 75µs (i.e. 13kS/s), and has a bandwidth of >5GHz; it measures risetimes of <0.14ns.
Back in the 80s I used a top-of-the-range HP 1GHz scope, which sampled at 25MS/s.
Nowadays you can see that principle in action in various scopes with modes called various things like Equivalent Time Sampling, and in the mixer of every SDR dongle (multiGHz inputs sampled at ~10MS/s).
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And what has this to do with the topic discussed here? The equivalent sample rate has to satisfy Nyquist no matter what. And thankfully, nobody has to resort to the ETS crouch for bandwidths up to a couple of GHz anymore nowadays.
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Last week there was an old 1GHz Tek scope auctioned. It went for £1250+35%, which is out of my range. So, yes, some of us do have to resort to ETS - and with skill and imagination we manage to find ways to achieve our ends with tools that many regard as "inadequate".
--- Quote ---
--- Quote from: tggzzz on April 09, 2023, 01:17:36 pm --- [1] Standard interview question... You have an audio signal transmitted on a 10MHz carrier. What is the minimum sampling rate you can use?
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Funny that you feel like asking that question in reply to my post of all things.
[1] I have demonstrated several times, how to analyze narrowband signals by means of down-conversion by undersampling, e.g. here:
https://www.eevblog.com/forum/testgear/siglent-sds2000x-hd-12bit-(published-for-chinese-domestic-market-only)/msg4320658/#msg4320658
… so what was the intention of your reply? Just to say "no" … or did you want to add some confusion for those who are less familiar with modern DSOs?
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To point out that the number of samples/second is a relatively unimportant metric of a scope's performance and usefulness. As you know, front end bandwidth is far more important.
But too many beginners (and apparently experienced people) focus on the sampling rate and think that 1GS/s is automatically better than 250MS/s. My examples are designed to highlight the orthogonality of Hz and S/s.
nctnico:
--- Quote from: tggzzz on April 09, 2023, 05:44:25 pm ---But too many beginners (and apparently experienced people) focus on the sampling rate and think that 1GS/s is automatically better than 250MS/s.
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For a general purpose oscilloscope used for measurements up to 200 to 300 MHz that is simply true. Any reasonable new DSO you can buy nowadays supports at least 1Gs/s for at least 1 channel. Beyond that you can start to weigh things like budget versus requirements but at that point you are looking at measurements that are more specialistic.
wasedadoc:
--- Quote from: tggzzz on April 09, 2023, 01:17:36 pm ---Standard interview question... You have an audio signal transmitted on a 10MHz carrier. What is the minimum sampling rate you can use?
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Standard answer from final year university student. "We haven't done that yet." How many times did I hear that in response to questions?
2N3055:
--- Quote from: tggzzz on April 09, 2023, 04:42:16 pm ---
A revealing response to the technical points.
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I agree. Your post is exactly that.. Good point there... Hence OMG... because I have nothing else to say to your endless patronizing us with wrong points...
I know what sampling scopes are, how they work and what are they used for.
That whole topic is IRRELEVANT to discussion which REAL time sampling scope in entry level price range is best choice for OP.. We don't care for another incorrect lecture about sampling scopes...
And I'm going to repeat: To look at 10 MHz modulated signal you need to obey Nyquist and sample at more than twice the frequency of highest frequency in a signal. That is 10MHz here (plus a bit more for sidebands)... So something about 25MS/s or up...
Your questions begs that answer.
If you weren't try to be smartarse you wouldn't ask a smartarse "trick question" but a one that is technically and factually correct.
If you wanted and answer to "how can you extract audio signal from 10 MHz carrier and what sampling rate is sufficient for that" than ask that..
Idiotic questions get stupid answers....
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